1. Field of the Invention
The present invention relates to conformance additives and methods of making such additives, to conformance treatment fluids made therefrom and methods of making such fluids, to methods of modifying a well fluid with such additives, to methods of operating and a well using such additives, and to methods of improving conformance in a well using such additives and/or fluids. In another aspect, the present invention relates to conformance additives comprising polymer, crosslinking agent, and a filter aid, to conformance treatment fluids made therefrom and methods of making such fluids, to methods of modifying a well fluid, to methods of operating a well, and to methods of improving conformance in a well. In even another aspect, the present invention relates to conformance additives comprising a dry mixture of polymer, crosslinking agent, and a filter aid, to conformance treatment fluids made therefrom and methods of making such fluids, to methods of modifying a well fluid, to methods of operating a well, and to methods of improving conformance in a well. In still another aspect, the present invention relates to conformance additives comprising polymer and diatomaceous earth (“DE”), to conformance treatment fluids made therefrom, to methods of modifying a well fluid, to methods of operating a well, and to methods of improving conformance in a well.
2. Description of the Related Art
In the production of hydrocarbons from subterranean hydrocarbon bearing formations, poor vertical conformance results from the vertical juxtaposition of relatively high permeability geologic zones to relatively low permeability zones within the subterranean formation. Poor areal conformance results from the presence of high permeability streaks and high permeability anomalies within the formation matrix, such as vertical fractures and networks of the same, which have very high permeability relative to the formation matrix. Fluids generally exhibit poor flow profiles and sweep efficiencies in subterranean formations having poor vertical or areal conformance. Poor conformance is particularly a problem where vertical heterogeneity and/or fracture networks or other structural anomalies are in fluid communication with a subterranean wellbore across which fluids are injected or produced.
The prior art is replete with a number of attempts to remedy conformance problems. For example, U.S. Pat. Nos. 3,762,476; 3,981,363; 4,018,286; and 4,039,029 to Gall or Gall et al describe various processes wherein gel compositions are formed in high permeability zones of subterranean formations to reduce the permeability therein. According to U.S. Pat. No. 3,762,476, a polymer such as polyacrylamide is injected into a formation followed sequentially by a crosslinking agent. The sequentially injected slugs are believed to permeate the treatment zone of the formation and gel in situ.
U.S. Pat. Nos. 4,683,949 and 4,744,419 both to Sydansk et al., both note that it is generally held that effective polymer/crosslinking agent systems necessitate sequential injection of the gel components because gel systems mixed on the surface often set up before they can effectively penetrate the treatment region. Both Sydansk et al. patents further note that in practice, treatments such as that disclosed in U.S. Pat. No. 3,762,476 using sequentially injected gel systems have proven unsatisfactory because of the inability to achieve complete mixing and gelation in the formation. As a result, gels only form at the interface of the unmixed gel components and often in regions remote from the desired treatment region.
Both of the Sydansk et al. patents purport to overcome a then-existing need in the art for a gelation process capable of forming gels having a predetermined gelation rate, strength, and stability to satisfy the particular demands of a desired treatment region in a subterranean hydrocarbon-bearing formation, through the use of a high molecular weight water-soluble acrylamide polymer, a chromium III/carboxylate complex cross-linking agent.
U.S. Pat. No. 5,377,760 to Merrill notes that while the polymer system of Sydansk et al. '949 was an improvement over prior art systems which required sequential injection of the polymer components, difficulty was still encountered in employing the '949 polymer system to plug large fissures because the larger masses of polymer required often lack the necessary strength to resist the pressures to which they are exposed. Merrill proposes the incorporation of fibers in the polymer by mixing the fibers with the polymer solution at the surface.
U.S. Pat. No. 3,701,384 discloses a method of sealing thief zones in a subterranean formation by plugging pores with a solid material. A slurry of finely divided inorganic solids is injected into the formation together with an aqueous colloidal dispersion of a water-insoluble metal hydroxide in a dilute aqueous solution of a high-molecular-weight organic polymeric polyelectrolyte. The preferred polymer solution contains between about 0.01 and about 0.2 percent by weight of high molecular weight polyacrylamide or hydrolyzed polyacrylamide. At these concentrations, the dissolved polymer causes the suspended solids to flocculate, thereby blocking pores in the formation. The tested inorganic solids which interacted with the polymer solution to form strong solids included finely ground asbestos fibers and magnesium oxide. However, asbestos is undesirable for use today, due to its carcinogenicity.
Another approach taken by the prior art is to pump a slurry containing a mixture of flexible fibers and a bonding agent into highly permeable portions of a formation interval. An agent which precipitates or gels the bonding agent is then injected into the interval. The goal of the method is to build up a filter cake of fibers on the permeable formation as a result of the fibers being deposited out of the slurry as the slurry flows through, the permeable formation, and then bond the fibers of the filter cake in place. Examples of such a method are disclosed in U.S. Pat. Nos. 3,593,798, 3,949,811 and 3,462,958.
Larger fissures are bridged according to the disclosure of U.S. Pat. No. 2,708,973 by setting fibrous plants in place in the fissure, after which cement is added, thereby building on the framework of the plants. While such a method can bridge larger gaps, the process is impractical for use in deep formations that extend over a large area.
U.S. Pat. No. 3,374,834 discloses a method of stabilizing earth formations by injecting an aqueous solution of gelling material which contains finely divided inert solids and needle-like crystals of silicate materials which act as a suspending agent to prevent premature settling out of the solids. The resulting gel does not, however, provide the desired combination of strength, economy, ease of mixing and ability to be readily introduced into a formation.
As an advance over the above prior art, U.S. Pat. No. 6,102,121, issued Aug. 15, 2000, to Boyce D. Burts, Jr., for “Conformance improvement additive, conformance treatment fluid made therefrom, method of improving conformance in a subterranean formation,” discloses an additive including a dry mixture of water soluble crosslinkable polymer, a crosslinking agent, and a reinforcing material of fibers and/or comminuted plant materials. The method of forming a fluid includes contacting the additive with water or an aqueous solution, with a method of treating the formation further including the step of injecting the fluid into the formation.
While not believed to be related prior art because they relate to different types of well operations, for completeness, attention is directed to five other similar “dry mixture” patents by Boyce D. Burts, Jr., which were filed on the same day (Oct. 31, 1997) as the '121 Patent: U.S. Pat. No. 6,218,343, issued Apr. 17, 2001, for “Additive for, treatment fluid for, and method of plugging a tubing/casing annulus in a well bore,” U.S. Pat. No. 6,098,712, issued Aug. 8, 2000, for “Method of plugging a well,” U.S. Pat. No. 6,016,879, issued Jan. 25, 2000, for “Lost circulation additive, lost circulation treatment fluid made therefrom, and method of minimizing lost circulation in a subterranean formation,” U.S. Pat. No. 6,016,871, issued Jan. 25, 2000, for “Hydraulic fracturing additive, hydraulic fracturing treatment fluid made therefrom, and method of hydraulically fracturing a subterranean formation,” and U.S. Pat. No. 6,016,869, issued Jan. 25, 2000, for “Well kill additive, well kill treatment fluid made therefrom, and method of killing a well.”
A number of patents discuss the use of diatomaceous earth (“DE”) in a well operation.
U.S. Pat. No. 3,380,542, issued Apr. 30, 1968 to Clear, for restoring lost circulation discloses a oil-based drilling fluid, containing a slurry of diatomite and asbestos, used to restore lost circulation during well drilling operations.
U.S. Pat. No. 4,369,844, issued Jan. 25, 1983 to Clear, discloses that various formation sealing agents have been used in the art to form formation seals and/or filter cakes on the wall of a well bore, including diatomaceous earth.
U.S. Pat. No. 4,110,225, issued Aug. 29, 1978 to Cagle, discloses that zones of lost circulation and other undesired fluid communication channels into a wellbore are sealed by isolating a volume in the well including such a zone and applying greater than formation pressure to a novel slurry spotted in the zone until it hardens into a solid, drillable seal. The slurry contains per barrel from 5-50 pounds diatomaceous mix, from about 35 to about 350 pounds of oil well cement, and at a minimum about 5 to 6 pounds of a flake type lost-circulation agent. This '225 patent cites a number of patents that disclose cement/diatomaceous earth compositions, including U.S. Pat. Nos. 2,585,336; 2,793,957; 2,961,044; 3,467,198; and 3,558,335.
Regarding these patents, the '225 patent notes the following:                Regarding U.S. Pat. No. 2,585,336, the '225 patent notes, “a mixture is made using from 2% to 100% diatomaceous earth, compared to the content of the cement in the slurry. The aim of the inventors was to prevent perlite from settling and to produce a lightweight cement. The diatomaceous earth-cement described in the disclosure is a mixture of Portland cement, perlite and diatomaceous earth, lime, and asbestos fibers.”        Regarding U.S. Pat. No. 2,793,957, the '225 patent notes, “refers to a highly permeable cement formed by use of the same basic mixtures of diatomaceous earth with Portland cement, the diatomaceous earth present being from five to seven times the proportion of the Portland cement in the slurry. The aim of the inventors was to produce a light highly permeable cement, entirely opposite to the purpose of my invention.”        Regarding U.S. Pat. No. 2,961,044, the '225 patent notes, “discusses and claims a cement composition which has diatomaceous earth in the amounts of from 30% to 70% of the Portland cement. The reason for using the diatomaceous earth was to prevent the strength retrogression of a salt-saturated cement. Thus, while Shell wishes (among other uses) to employ his mixture for squeeze cementing, he produces a relatively high-strength cement plug. There is a real tendency when redrilling such a plug for the bit to be deflected or sidetracked so that the new hole is beside rather than through the bore and the seal is ineffective. This is completely different from my invention which minimizes such tendency by producing a plug at least as drillable as the formation in which it is set. Also, Shell is directed to operations using salt-saturated cement slurries, while I prefer using a fresh or brackish water slurry. I employ lost-circulation agents; he makes no teaching of using such additives. Accordingly, his teaching is quite far from mine.”        Regarding both U.S. Pat. Nos. 3,467,198 and 3,558,335, the '225 patent notes, “describe cement compositions having diatomaceous mix present in the amounts from 0.5% to 10% of the amount of Portland cement present to prevent solids-settling.”        
U.S. Pat. No. 4,369,844, issued Jan. 25, 1983 to Clear, discloses slurries to seal permeable earth formations encountered in the drilling of wells, comprising finely divided paper, diatomaceous earth, and in a further embodiment, lime. A slug of the slurry is spotted at the locus of the permeable formation and defluidized to form a formation seal on which a mud sheath is then deposited.
U.S. Pat. No. 4,505,751, issued Mar. 19, 1985, discloses a silicate/silica cement in oil field applications, including diatomaceous earth as a species of silica compound.
While not believed to be analogous prior art because it relates to earthen pits (for example a ditch) and not to subterrean wellbores nor well operations, U.S. Pat. No. 5,947,644, issued Sep. 7, 1999 to Gibbons et al., is included herein for completeness because it discloses a gelable slurry of aqueous solvent, a crosslinkable polymer, a crosslinking agent, and unconsolidated solids such as diatomaceous earth. This gelable slurry is placed in an earthen pit and allowed to form into a fluid impermeable barrier wall in the earthen pit. The polymer serves to bind the unconsolidated solids to convert the gelable slurry to a nondeformable gelled continuum of consolidated solids, which forms the barrier wall in the earthen pit. As disclosed in the '644 Patent in the Summary of the Invention section, at col. 1, lines 57-67, this gelable slurry is prepared by first forming a liquid gelation solution of the polymer and crosslinking agent, to which is subsequently mixed with the unconsolidated solids, or alternatively, by sequentially mixing the aqueous solvent, crosslinkable polymer, and polymer crosslinking agent with the unconsolidated solids.
However, in spite of the advancements in the prior art, there still need for further innovation in the conformance.
These needs in the art will become apparent to those of skill in the art upon review of this specification, including its drawings and claims.